Inline Editing in lightning-datatable in LWC Salesforce

public class LWCInlineCtrl {
    @AuraEnabled(Cacheable = true)
    public static List<Contact> getContacts() {
        return [SELECT Id, Name, FirstName, LastName, Phone, Email 
                FROM Contact 
                WHERE Email != null 
                AND Phone != null 
                ORDER BY CreatedDate limit 20];
    }
}

<template>

     <!------Header------->
    <div class="slds-tabs_card">
		<div class="slds-page-header">
			<div class="slds-page-header__row">
				<div class="slds-page-header__col-title">
					<div class="slds-media">
						<div class="slds-media__figure">
							<span class="slds-icon_container slds-icon-standard-opportunity">
								 <lightning-icon icon-name="standard:recipe" alternative-text="recipe" title="recipe"></lightning-icon>
                            </span>
						</div>
						<div class="slds-media__body">
							<div class="slds-page-header__name">
								<div class="slds-page-header__name-title">
									<h1>
										<span>Inline Editing in lightning-datatable in LWC Salesforce </span>
										<span class="slds-page-header__title slds-truncate" title="Recently Viewed">TechDicer</span>
									</h1>
								</div>
							</div>
						</div>
					</div>
				</div>
			</div>
		</div>
	</div> <br/>
    <!------/Header------->


    <lightning-card title="Inline Editing in lightning-datatable in LWC Salesforce" icon-name="standard:contact">
        <template if:true={contacts.data}>
            <lightning-datatable key-field="Id" 
                                 data={contacts.data} 
                                 columns={columns} 
                                 onsave={handleSave}
                                 draft-values={saveDraftValues} 
                                 hide-checkbox-column 
                                 show-row-number-column>
            </lightning-datatable>
        </template>
    </lightning-card>
</template>

import { LightningElement, wire, track } from 'lwc';
import getContacts from '@salesforce/apex/LWCInlineCtrl.getContacts';
import { updateRecord } from 'lightning/uiRecordApi';
import { ShowToastEvent } from 'lightning/platformShowToastEvent';
import { refreshApex } from '@salesforce/apex';

// columns
const columns = [
    {
        label: 'Name',
        fieldName: 'Name',
        type: 'text',
    }, {
        label: 'FirstName',
        fieldName: 'FirstName',
        type: 'text',
        editable: true,
    }, {
        label: 'LastName',
        fieldName: 'LastName',
        type: 'text',
        editable: true,
    }, {
        label: 'Phone',
        fieldName: 'Phone',
        type: 'phone',
        editable: true
    }
];

export default class LWCInline extends LightningElement {
    columns = columns;
    @track contacts;
    saveDraftValues = [];

    @wire(getContacts)
    contactData(result) {
        this.contacts = result;
        if (result.error) {
            this.contacts = undefined;
        }
    };

    handleSave(event) {
        this.saveDraftValues = event.detail.draftValues;
        const recordInputs = this.saveDraftValues.slice().map(draft => {
            const fields = Object.assign({}, draft);
            return { fields };
        });

        // Updateing the records using the UiRecordAPi
        const promises = recordInputs.map(recordInput => updateRecord(recordInput));
        Promise.all(promises).then(res => {
            this.ShowToast('Success', 'Records Updated Successfully!', 'success', 'dismissable');
            this.saveDraftValues = [];
            return this.refresh();
        }).catch(error => {
            this.ShowToast('Error', 'An Error Occured!!', 'error', 'dismissable');
        }).finally(() => {
            this.saveDraftValues = [];
        });
    }

    ShowToast(title, message, variant, mode){
        const evt = new ShowToastEvent({
                title: title,
                message:message,
                variant: variant,
                mode: mode
            });
            this.dispatchEvent(evt);
    }

    // This function is used to refresh the table once data updated
    async refresh() {
        await refreshApex(this.contacts);
    }
}